An ion with mass number 37 possesses one unit of negative charge. If the ion contains 11.1% more neutrons than the electrons, find the symbol of the ion.

Let the number of electrons in the ion carrying a negative charge be x. Then,
Number of neutrons present
= x + 11.1% of x
= x + 0.111 x
= 1.111 x
Number of electrons in the neutral atom = (x – 1)
(When an ion carries a negative charge, it carries an extra electron)
∴ Number of protons in the neutral atom = x – 1
Given,
Mass number of the ion = 37
∴ (x – 1) + 1.111x = 37
2.111x = 38 x
= 18
∴The symbol of the ion is ${}_{17}^{37}{\text{Cl}}^{-}$